Welcome to Airbnb and the host community!
Be sure you learn how to be a host before jumping in. Read everything you can on the Airbnb platform and watch the instructional videos. If you can find an Airbnb SuperHost in your area who can mentor you, that could be a helpful.
Do not use the Instant Book feature until you know how it works and are comfortable with it.
Make sure your listing accurately reflects what you have to offer.
Speed up your timeline and get the room ready for the guest that booked it! That may be the easiest thing to do!
If you absolutely can't have the room ready in time, call the guest and call Airbnb and explain the situation. The guest may graciously agree to seek other lodging and Airbnb may graciously agree to refund their booking fee. Don't cancel as a host until you understand and the consequences.
Lastly, do you have the permission of your landlord to host Airbnb guests in your new apartment home? Read the terms of your rental agreement carefully. If you can't host in the space, you will need to de-list your offering.